The present invention relates to an image forming apparatus and process cartridge used for, for example, a monochrome or color printer, copying machine, facsimile, and the like.
An image forming apparatus such as an electrophotographic copier, an electrophotographic printer or the like, employs a method of obtaining printed matters through steps of: homogeneously charging a surface of a photosensitive member; forming an electrostatic latent image by exposure; developing the latent image by attaching toner thereto; transferring the toner on the surface of the photosensitive member to a subject to accept transfer such as paper; and fixing the toner image on the subject. In each step, a member that is directly pressed onto and slides on the photosensitive member, such as a charging roller, a developing roller, a transfer roller, a cleaning roller, and the like, may be used. It is desirable to use a member having each respective function that does not easily damage the surface of the photosensitive member, and does not contaminate the photosensitive member. For example, a conductive developing roller having an appropriate elasticity generally is used, in a non-magnetic one-component (contact) developing process, which is employed in a copier, printer, or the like, which forms a full color image by image forming process using an electrophotographic method. The generally usable conductive elastic member of this kind includes, for example, a composition in which a conductivity-providing agent is contained in natural rubber or various kinds of synthetic rubber. For example, JP 3-7966A discloses the use of an EPDM (ethylene-propylene-diene copolymer), JP 4-328162A discloses the use of a silicone rubber, and JP 5-117434A discloses the use of an urethane rubber.
Furthermore, as the conductive roller used for the charging roller or the transfer roller, JP 7-281502A discloses the use of conductive fluorocarbon silicone rubber and N-methyl methoxized nylon, as examples; and JP 8-15950A discloses the use of a silicone rubber foam, as an example.
Among the rollers in contact with the photosensitive member, the rollers using silicone rubber or urethane rubber are more excellent in stability of the resistance value in manufacturing as compared with the roller using EPDM. However, when either silicone rubber or urethane rubber is used in contact with the photosensitive member, a plasticizer or a softener, which is contained in the above-mentioned rubbers, may bleed from the surface of the roller using silicone rubber or urethane rubber to contaminate the photosensitive member. Furthermore, if sulfur or a derivative thereof is used for a vulcanizing agent for rubber, a remaining component of such a vulcanizing agent may contaminate the photosensitive member.
In order to solve such problems, JP 5-125209A or JP 7-146602 discloses a technique of coating the surface of roller, however, such techniques are not sufficient.
In the current distributing products, such a problem is solved by providing a disjunction mechanism that does not bring each roller into contact with the photosensitive member other than at the development time. However, such a disjunction mechanism makes the apparatus complicated, and raises the cost.
A general cartridge used in a monochrome printer is configured by integrating a toner hopper, a developer, and a photosensitive member into one piece, and thus it is excellent in a maintenance property. However, in most color cartridges, in order to solve the above-mentioned problems, a developer and the photosensitive member are formed separately. Therefore, it is difficult to satisfy both the high quality image by a developing roller made of silicone rubber and the excellent maintenance property that is the same level as that of monochrome cartridges.
It is an object of the present invention to provide an image forming apparatus and a process cartridge capable of satisfying both the high quality image and the improved maintenance property with a simple configuration.
In order to attain the above-mentioned object, a first configuration of an image forming apparatus according to the present invention includes a photosensitive member and members rotating in contact with the photosensitive member. When an image forming operation starts from a standstill, the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated. According to the first configuration of the image forming apparatus, it is possible to scrape off only a contaminated portion on the contacting portion between the members rotating in contact with the photosensitive member and the photosensitive member by the member that is a contamination source itself, while the structure is kept simple. Thus, even if urethane rubber or silicone rubber is used for a material of the members, for example, a charging roller, a developing roller, or the like, which rotate in contact with the photosensitive member, it is possible to prevent the contamination of the photosensitive member. Furthermore, it is not necessary to form a developer and a photosensitive member as separate units. Therefore, according to first configuration of the image forming apparatus, it is possible to attain the image forming apparatus capable of satisfying both the high quality image and the improved maintenance property with a simple configuration.
Furthermore, a second configuration of an image forming apparatus according to the present invention includes a photosensitive member and members rotating in contact with the photosensitive member. Before the photosensitive member starts to be rotated, a reversed bias voltage that is an opposite voltage to the bias voltage at usual development time is applied between the members rotating in contact with the photosensitive member and the photosensitive member. According to the second configuration of the image forming apparatus, charges are filled onto the contaminated portion on the photosensitive member, and thus it is possible to suppress the appearance of a hollow white printing on a half tone image.
Furthermore, it is preferable in the second configuration of the image forming apparatus according to the present invention that an application time of the reversed bias voltage is 0.01-2.0 seconds.
Furthermore, it is preferable in the second configuration of the image forming apparatus according to the present invention that the application time of the reversed bias voltage is changed in accordance with the number of pages printed. In this case, it is further preferable that the application time of the reversed bias voltage is reduced each time the number of pages printed reaches a predetermined number. When the number of pages printed is increased and toner is deteriorated, the deteriorated toner is attached to the portion to which the reversed bias voltage is applied, on the photosensitive member. As a result, black lines are generated.
Furthermore, in this case, it is further preferable that the changing degree of the application time of the reversed bias voltage is varied in accordance with the toner being applied whether black toner or cyan toner, magenta toner, and yellow toner. This is because the black toner contains a carbon pigment and has different characteristics from those of cyan toner, magenta toner, and yellow toner (i.e., color toner).
Furthermore, a third configuration of an image forming apparatus according to the present invention includes a photosensitive member and members rotating in contact with the photosensitive member. When an image forming operation starts from a standstill, the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated, and while the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated, a reversed bias voltage that is opposite voltage to the bias voltage at usual development time is applied between the members rotating in contact with the photosensitive member and the photosensitive member. According to the third configuration of the image forming apparatus, while the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated, toner can be prevented from scattering and the contaminants can be attracted. This effect is exhibited significantly in a case where the member rotating in contact with the photosensitive member is a developing member on the surface of which toner exists in the form of a thin film.
Furthermore, it is preferable that the third configuration of the image forming apparatus according to the present invention further includes a member for removing electricity, which is in contact with the photosensitive member, so as to remove electricity after transfer. With such a preferred configuration, since excess charges on the photosensitive member can be removed, it is possible to prevent black lines from appearing on a non-printed part of the recording paper.
Furthermore, it is preferable in the first or third configuration of the image forming apparatus according to the present invention that a time for which the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated is 0.01-2.0 seconds. When the time is less than 0.01 seconds, the effect of scraping off the contaminants is lowered; and when the time is more than 2.0 seconds, the lifetime of each roller is shortened and it takes an unnecessarily longer time to perform a first copy.
Furthermore, it is preferable in the first or third configuration of the image forming apparatus according to the present invention that the time for which the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated is changed in accordance with the number of pages printed. In this case, it is further preferable that the time for which the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated is reduced each time the number of pages printed reaches the predetermined number. In this case, it is still further preferable that the changing degree of the time for which the members rotating in contact with the photosensitive member before the photosensitive member starts to be rotated is varied in accordance with whether toe toner is black toner or cyan toner, magenta toner, and yellow toner.
Furthermore, it is preferable in the second or third configuration of the image forming apparatus according to the present invention that the absolute value of the reversed bias voltage is 5-300 V. When the value is less than 5V, it is not possible to suppress the scattering of toner sufficiently; and when the value is more than 300V, the contamination by toner to the member rotating in contact with the photosensitive member is increased, thus shortening the lifetime of the member rotating in contact with the photosensitive member.
Furthermore, it is preferable in the second configuration of the image forming apparatus according to the present invention that the amount of the reversed bias voltage is changed in accordance with the number of pages printed. In this case, it is further preferable that the amount of reversed bias voltage is reduced each time the number of pages printed reaches a predetermined number. In this case, it is still further preferable that the changing degree of the reversed bias voltage is changed in accordance with whether the toner is black toner or cyan toner, magenta toner, and yellow toner.
Furthermore, it is preferable in the first or third configuration of the image forming apparatus according to the present invention that the members rotating in contact with the photosensitive member are rollers made of rubber and formed around an axis core, and wherein the rubber has a hardness of 30-80 degrees, a thickness of 0.5-7 mm, and a pressing force with respect to the photosensitive member of 0.5-1.2 kg. In this case, it is further preferable that the rubber has a hardness of 40-70 degrees, and a thickness of 1-5 mm.
Furthermore, in the first to third configurations of the image forming apparatus according to the present invention, the members rotating in contact with the photosensitive member include, for example, a charging roller or a developing roller. In this case, silicone rubber or urethane robber is used for the material of the charging roller or the developing roller.
Furthermore, a process cartridge of a first configuration according to the present invention includes a photosensitive member and members rotating in contact with the photosensitive member. When an image forming operation starts from a standstill, the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated.
Furthermore, a process cartridge of a second configuration according to the present invention includes a photosensitive member and members rotating in contact with the photosensitive member. Before the photosensitive member starts to be rotated, a reversed bias voltage that is an opposite voltage to the bias voltage at usual development time is applied between the members rotating in contact with the photosensitive member and the photosensitive member.
Furthermore, it is preferable in the second configuration of the process cartridge according to the present invention that an application time of the reversed bias voltage is 0.01-2.0 seconds.
Furthermore, it is preferable in the second configuration of the process cartridge according to the present invention that the application time of the reversed bias voltage is changed in accordance with the number of pages printed. In this case, it is further preferable that the application time of the reversed bias voltage is reduced each time the number of pages printed reaches a predetermined number.
Furthermore, a process cartridge of a third configuration according to the present invention includes a photosensitive member and members rotating in contact with the photosensitive member. When an image forming operation starts from a standstill, the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated, and while the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated, a reversed bias voltage that is opposite voltage to the bias voltage at usual development time is applied between the members rotating in contact with the photosensitive member and the photosensitive member.
Furthermore, it is preferable that the third configuration of the process cartridge according to the present invention further includes a member for removing electricity, which is in contact with the photosensitive member, so as to remove electricity after transfer.
Furthermore, it is preferable in the first or third configuration of the process cartridge according to the present invention that a time for which the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated is 0.01-2.0 seconds.
Furthermore, it is preferable in the first or third configuration of the process cartridge according to the present invention that the time for which the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated is changed in accordance with the number of pages printed. In this case, it is further preferable that the time for which the members rotating in contact with the photosensitive member are rotated before the photosensitive member starts to be rotated is changed in accordance with the number of pages printed.
Furthermore, it is preferable in the second or third configuration of the process cartridge according to the present invention that the absolute value of the reversed bias voltage is 5-300V.
Furthermore, it is preferable in the second configuration of the process cartridge according to the present invention that the amount of the reversed bias voltage is changed in accordance with the number of pages printed. In this case, it is preferable that the amount of reversed bias voltage is reduced each time the number of pages printed reaches a predetermined number.
Furthermore, it is preferable in the first or third configuration of the process cartridge according to the present invention that the members rotating in contact with the photosensitive member are rollers made of rubber and formed around an axis core, and wherein the rubber has a hardness of 30-80 degrees, a thickness of 0.5-7 mm, and a pressing force with respect to the photosensitive member of 0.5-1.2 kg. In this case, it is further preferable that the rubber has a hardness of 40-70 degrees, and a thickness of 1-5 mm.
Furthermore, in the first to third configurations of the process cartridge according to the present invention, the members rotating in contact with the photosensitive member include, for example, a charging roller or a developing roller. In this case, silicone rubber or urethane robber is used for the material of the charging roller or the developing roller.